diff --git a/src/ast/rewriter/pb2bv_rewriter.cpp b/src/ast/rewriter/pb2bv_rewriter.cpp
index 37c87cd5b..6ba55d12a 100644
--- a/src/ast/rewriter/pb2bv_rewriter.cpp
+++ b/src/ast/rewriter/pb2bv_rewriter.cpp
@@ -49,6 +49,7 @@ struct pb2bv_rewriter::imp {
         expr_ref_vector m_args;
         rational     m_k;
         vector<rational> m_coeffs;
+        bool m_enable_card;
 
         template<lbool is_le>
         expr_ref mk_le_ge(expr_ref_vector& fmls, expr* a, expr* b, expr* bound) {
@@ -238,12 +239,13 @@ struct pb2bv_rewriter::imp {
             pb(m),
             bv(m),
             m_trail(m),
-            m_args(m)
+            m_args(m),
+            m_enable_card(false)
         {}
 
         bool mk_app(bool full, func_decl * f, unsigned sz, expr * const* args, expr_ref & result) {
-            if (f->get_family_id() == pb.get_family_id()) {
-                mk_pb(full, f, sz, args, result);
+            if (f->get_family_id() == pb.get_family_id() && mk_pb(full, f, sz, args, result)) {
+                // skip
             }
             else if (au.is_le(f) && is_pb(args[0], args[1])) {
                 result = mk_le_ge<l_true>(m_args.size(), m_args.c_ptr(), m_k);
@@ -349,29 +351,36 @@ struct pb2bv_rewriter::imp {
             return false;
         }
 
-        void mk_pb(bool full, func_decl * f, unsigned sz, expr * const* args, expr_ref & result) {
+        bool mk_pb(bool full, func_decl * f, unsigned sz, expr * const* args, expr_ref & result) {
             SASSERT(f->get_family_id() == pb.get_family_id());
+            std::cout << "card: " << m_enable_card << "\n";
             if (is_or(f)) {
                 result = m.mk_or(sz, args);
             }
             else if (pb.is_at_most_k(f) && pb.get_k(f).is_unsigned()) {
+                if (m_enable_card) return false;
                 result = m_sort.le(full, pb.get_k(f).get_unsigned(), sz, args);
             }
             else if (pb.is_at_least_k(f) && pb.get_k(f).is_unsigned()) {
+                if (m_enable_card) return false;
                 result = m_sort.ge(full, pb.get_k(f).get_unsigned(), sz, args);
             }
             else if (pb.is_eq(f) && pb.get_k(f).is_unsigned() && pb.has_unit_coefficients(f)) {
+                if (m_enable_card) return false;
                 result = m_sort.eq(full, pb.get_k(f).get_unsigned(), sz, args);
             }
             else if (pb.is_le(f) && pb.get_k(f).is_unsigned() && pb.has_unit_coefficients(f)) {
+                if (m_enable_card) return false;
                 result = m_sort.le(full, pb.get_k(f).get_unsigned(), sz, args);
             }
             else if (pb.is_ge(f) && pb.get_k(f).is_unsigned() && pb.has_unit_coefficients(f)) {
+                if (m_enable_card) return false;
                 result = m_sort.ge(full, pb.get_k(f).get_unsigned(), sz, args);
             }
             else {
                 result = mk_bv(f, sz, args);
             }
+            return true;
         }
    
         // definitions used for sorting network
@@ -396,6 +405,12 @@ struct pb2bv_rewriter::imp {
         void mk_clause(unsigned n, literal const* lits) {
             m_imp.m_lemmas.push_back(mk_or(m, n, lits));
         }        
+
+        void enable_card(bool f) {
+            std::cout << "set " << f << "\n";
+            m_enable_card = f;
+            m_enable_card = true;
+        }
     };
 
     struct card2bv_rewriter_cfg : public default_rewriter_cfg {
@@ -407,6 +422,7 @@ struct pb2bv_rewriter::imp {
             return m_r.mk_app_core(f, num, args, result);
         }
         card2bv_rewriter_cfg(imp& i, ast_manager & m):m_r(i, m) {}
+        void enable_card(bool f) { m_r.enable_card(f); }
     };
     
     class card_pb_rewriter : public rewriter_tpl<card2bv_rewriter_cfg> {
@@ -415,6 +431,7 @@ struct pb2bv_rewriter::imp {
         card_pb_rewriter(imp& i, ast_manager & m):
             rewriter_tpl<card2bv_rewriter_cfg>(m, false, m_cfg),
             m_cfg(i, m) {}
+        void enable_card(bool f) { m_cfg.enable_card(f); }
     };
 
     card_pb_rewriter m_rw;
@@ -424,9 +441,13 @@ struct pb2bv_rewriter::imp {
         m_fresh(m),
         m_num_translated(0), 
         m_rw(*this, m) {
+        m_rw.enable_card(p.get_bool("cardinality_solver", false));
     }
 
-    void updt_params(params_ref const & p) {}
+    void updt_params(params_ref const & p) {
+        m_params.append(p);
+        m_rw.enable_card(m_params.get_bool("cardinality_solver", false));        
+    }
     unsigned get_num_steps() const { return m_rw.get_num_steps(); }
     void cleanup() { m_rw.cleanup(); }
     void operator()(expr * e, expr_ref & result, proof_ref & result_proof) {
diff --git a/src/sat/card_extension.cpp b/src/sat/card_extension.cpp
index 2af1a5b5e..756e9642c 100644
--- a/src/sat/card_extension.cpp
+++ b/src/sat/card_extension.cpp
@@ -144,12 +144,14 @@ namespace sat {
     }
 
     void card_extension::watch_literal(card& c, literal lit) {
+        TRACE("sat", tout << "watch: " << lit << "\n";);
         init_watch(lit.var());
         ptr_vector<card>* cards = m_var_infos[lit.var()].m_lit_watch[lit.sign()];
         if (cards == 0) {
             cards = alloc(ptr_vector<card>);
             m_var_infos[lit.var()].m_lit_watch[lit.sign()] = cards;
         }
+        TRACE("sat", tout << "insert: " << lit.var() << " " << lit.sign() << "\n";);
         cards->push_back(&c);
     }
 
@@ -436,7 +438,9 @@ namespace sat {
         return p;        
     }
 
-    card_extension::card_extension(): m_solver(0) {}
+    card_extension::card_extension(): m_solver(0) {        
+        TRACE("sat", tout << this << "\n";);
+    }
 
     card_extension::~card_extension() {
         for (unsigned i = 0; i < m_var_infos.size(); ++i) {
@@ -537,7 +541,10 @@ namespace sat {
 
     void card_extension::asserted(literal l) {
         bool_var v = l.var();
+        if (v >= m_var_infos.size()) return;
         ptr_vector<card>* cards = m_var_infos[v].m_lit_watch[!l.sign()];
+        TRACE("sat", tout << "retrieve: " << v << " " << !l.sign() << "\n";);
+        TRACE("sat", tout << "asserted: " << l << " " << (cards ? "non-empty" : "empty") << "\n";);
         if (cards != 0  && !cards->empty() && !s().inconsistent())  {
             ptr_vector<card>::iterator it = cards->begin(), it2 = it, end = cards->end();
             for (; it != end; ++it) {
@@ -545,7 +552,7 @@ namespace sat {
                 if (value(c.lit()) != l_true) {
                     continue;
                 }
-                switch (add_assign(c, l)) {
+                switch (add_assign(c, ~l)) {
                 case l_false: // conflict
                     for (; it != end; ++it, ++it2) {
                         *it2 = *it;
@@ -579,6 +586,7 @@ namespace sat {
     }
 
     void card_extension::pop(unsigned n) {        
+        TRACE("sat", tout << "pop:" << n << "\n";);
         unsigned new_lim = m_var_lim.size() - n;
         unsigned sz = m_var_lim[new_lim];
         while (m_var_trail.size() > sz) {
@@ -598,6 +606,21 @@ namespace sat {
     void card_extension::clauses_modifed() {}
     lbool card_extension::get_phase(bool_var v) { return l_undef; }
 
+    extension* card_extension::copy(solver* s) {
+        card_extension* result = alloc(card_extension);
+        result->set_solver(s);
+        for (unsigned i = 0; i < m_constraints.size(); ++i) {
+            literal_vector lits;
+            card& c = *m_constraints[i];
+            for (unsigned i = 0; i < c.size(); ++i) {
+                lits.push_back(c[i]);
+            }
+            result->add_at_least(c.lit().var(), lits, c.k());
+        }
+        return result;
+    }
+
+
     void card_extension::display_watch(std::ostream& out, bool_var v, bool sign) const {
         watch const* w = m_var_infos[v].m_lit_watch[sign];
         if (w) {
@@ -647,7 +670,7 @@ namespace sat {
         for (unsigned vi = 0; vi < m_var_infos.size(); ++vi) {
             card* c = m_var_infos[vi].m_card;
             if (c) {
-                display(out, *c, true);
+                display(out, *c, false);
             }
         }
         return out;
diff --git a/src/sat/card_extension.h b/src/sat/card_extension.h
index 1593ef26f..5c3f1e293 100644
--- a/src/sat/card_extension.h
+++ b/src/sat/card_extension.h
@@ -139,7 +139,7 @@ namespace sat {
     public:
         card_extension();
         virtual ~card_extension();
-        void    set_solver(solver* s) { m_solver = s; }
+        virtual void set_solver(solver* s) { m_solver = s; }
         void    add_at_least(bool_var v, literal_vector const& lits, unsigned k);
         virtual void propagate(literal l, ext_constraint_idx idx, bool & keep);
         virtual void get_antecedents(literal l, ext_justification_idx idx, literal_vector & r);
@@ -152,6 +152,7 @@ namespace sat {
         virtual lbool get_phase(bool_var v);
         virtual std::ostream& display(std::ostream& out) const;
         virtual void collect_statistics(statistics& st) const;
+        virtual extension* copy(solver* s);
     };
 
 };
diff --git a/src/sat/sat_extension.h b/src/sat/sat_extension.h
index f1a48c0a8..c065e132e 100644
--- a/src/sat/sat_extension.h
+++ b/src/sat/sat_extension.h
@@ -32,6 +32,7 @@ namespace sat {
     class extension {
     public:
         virtual ~extension() {}
+        virtual void set_solver(solver* s) = 0;
         virtual void propagate(literal l, ext_constraint_idx idx, bool & keep) = 0;
         virtual void get_antecedents(literal l, ext_justification_idx idx, literal_vector & r) = 0;
         virtual void asserted(literal l) = 0;
@@ -43,6 +44,7 @@ namespace sat {
         virtual lbool get_phase(bool_var v) = 0;
         virtual std::ostream& display(std::ostream& out) const = 0;
         virtual void collect_statistics(statistics& st) const = 0;
+        virtual extension* copy(solver* s) = 0;
     };
 
 };
diff --git a/src/sat/sat_params.pyg b/src/sat/sat_params.pyg
index 60708fd5c..940fa8c45 100644
--- a/src/sat/sat_params.pyg
+++ b/src/sat/sat_params.pyg
@@ -23,4 +23,5 @@ def_module_params('sat',
                           ('core.minimize', BOOL, False, 'minimize computed core'),
                           ('core.minimize_partial', BOOL, False, 'apply partial (cheap) core minimization'),
                           ('parallel_threads', UINT, 1, 'number of parallel threads to use'),
+                          ('cardinality_solver', BOOL, False, 'enable cardinality based solver'),
                           ('dimacs.core', BOOL, False, 'extract core from DIMACS benchmarks')))
diff --git a/src/sat/sat_solver.cpp b/src/sat/sat_solver.cpp
index 647c5f9ed..d4349d2c2 100644
--- a/src/sat/sat_solver.cpp
+++ b/src/sat/sat_solver.cpp
@@ -54,6 +54,7 @@ namespace sat {
         m_conflicts               = 0;
         m_next_simplify           = 0;
         m_num_checkpoints         = 0;
+        if (m_ext) m_ext->set_solver(this);
     }
 
     solver::~solver() {
@@ -84,13 +85,15 @@ namespace sat {
                 VERIFY(v == mk_var(ext, dvar));
             }
         }
-        unsigned sz = src.scope_lvl() == 0 ? src.m_trail.size() : src.m_scopes[0].m_trail_lim;
-        for (unsigned i = 0; i < sz; ++i) {
-            assign(src.m_trail[i], justification());
+        {
+            unsigned sz = src.scope_lvl() == 0 ? src.m_trail.size() : src.m_scopes[0].m_trail_lim;
+            for (unsigned i = 0; i < sz; ++i) {
+                assign(src.m_trail[i], justification());
+            }
         }
 
+        // copy binary clauses
         {
-            // copy binary clauses
             unsigned sz = src.m_watches.size();
             for (unsigned l_idx = 0; l_idx < sz; ++l_idx) {
                 literal l = ~to_literal(l_idx);
@@ -107,6 +110,7 @@ namespace sat {
                 }
             }
         }
+
         {
             literal_vector buffer;
             // copy clause
@@ -120,6 +124,10 @@ namespace sat {
                 mk_clause_core(buffer);
             }
         }
+
+        if (src.get_extension()) {
+            m_ext = src.get_extension()->copy(this);
+        }
     }
 
     // -----------------------
diff --git a/src/sat/sat_solver.h b/src/sat/sat_solver.h
index b42acc680..25c823446 100644
--- a/src/sat/sat_solver.h
+++ b/src/sat/sat_solver.h
@@ -74,7 +74,7 @@ namespace sat {
         reslimit&               m_rlimit;
         config                  m_config;
         stats                   m_stats;
-        extension *             m_ext;
+        scoped_ptr<extension>   m_ext;
         par*                    m_par;
         random_gen              m_rand;
         clause_allocator        m_cls_allocator;
@@ -251,6 +251,7 @@ namespace sat {
         void set_par(par* p);
         bool canceled() { return !m_rlimit.inc(); }
         config const& get_config() { return m_config; }
+        extension* get_extension() const { return m_ext.get(); }
         typedef std::pair<literal, literal> bin_clause;
     protected:
         watch_list & get_wlist(literal l) { return m_watches[l.index()]; }
diff --git a/src/sat/sat_solver/inc_sat_solver.cpp b/src/sat/sat_solver/inc_sat_solver.cpp
index 65a7b021c..e20ca9583 100644
--- a/src/sat/sat_solver/inc_sat_solver.cpp
+++ b/src/sat/sat_solver/inc_sat_solver.cpp
@@ -20,6 +20,7 @@ Notes:
 #include "solver.h"
 #include "tactical.h"
 #include "sat_solver.h"
+#include "card_extension.h"
 #include "tactic2solver.h"
 #include "aig_tactic.h"
 #include "propagate_values_tactic.h"
@@ -35,6 +36,8 @@ Notes:
 #include "ast_translation.h"
 #include "ast_util.h"
 #include "propagate_values_tactic.h"
+#include "sat_params.hpp"
+
 
 // incremental SAT solver.
 class inc_sat_solver : public solver {
@@ -68,7 +71,8 @@ class inc_sat_solver : public solver {
     typedef obj_map<expr, sat::literal> dep2asm_t;
 public:
     inc_sat_solver(ast_manager& m, params_ref const& p):
-        m(m), m_solver(p, m.limit(), 0),
+        m(m), 
+        m_solver(p, m.limit(), alloc(sat::card_extension)),
         m_params(p), m_optimize_model(false),
         m_fmls(m),
         m_asmsf(m),
@@ -79,6 +83,8 @@ public:
         m_dep_core(m),
         m_unknown("no reason given") {
         m_params.set_bool("elim_vars", false);
+        sat_params p1(m_params);
+        m_params.set_bool("cardinality_solver", p1.cardinality_solver());
         m_solver.updt_params(m_params);
         init_preprocess();
     }
@@ -86,6 +92,7 @@ public:
     virtual ~inc_sat_solver() {}
 
     virtual solver* translate(ast_manager& dst_m, params_ref const& p) {
+        std::cout << "translate\n";
         ast_translation tr(m, dst_m);
         if (m_num_scopes > 0) {
             throw default_exception("Cannot translate sat solver at non-base level");
@@ -210,8 +217,11 @@ public:
         sat::solver::collect_param_descrs(r);
     }
     virtual void updt_params(params_ref const & p) {
-        m_params = p;
+        m_params.append(p);
+        sat_params p1(p);
+        m_params.set_bool("cardinality_solver", p1.cardinality_solver());
         m_params.set_bool("elim_vars", false);
+        std::cout << m_params << "\n";
         m_solver.updt_params(m_params);
         m_optimize_model = m_params.get_bool("optimize_model", false);
     }
diff --git a/src/sat/tactic/goal2sat.cpp b/src/sat/tactic/goal2sat.cpp
index 72340bc1c..41fb4dfce 100644
--- a/src/sat/tactic/goal2sat.cpp
+++ b/src/sat/tactic/goal2sat.cpp
@@ -37,6 +37,7 @@ Notes:
 #include"tactic.h"
 #include"ast_pp.h"
 #include"pb_decl_plugin.h"
+#include"card_extension.h"
 #include<sstream>
 
 struct goal2sat::imp {
@@ -50,6 +51,7 @@ struct goal2sat::imp {
     };
     ast_manager &               m;
     pb_util                     pb;
+    sat::card_extension*        m_ext;
     svector<frame>              m_frame_stack;
     svector<sat::literal>       m_result_stack;
     obj_map<app, sat::literal>  m_cache;
@@ -67,6 +69,7 @@ struct goal2sat::imp {
     imp(ast_manager & _m, params_ref const & p, sat::solver & s, atom2bool_var & map, dep2asm_map& dep2asm, bool default_external):
         m(_m),
         pb(m),
+        m_ext(0),
         m_solver(s),
         m_map(map),
         m_dep2asm(dep2asm),
@@ -75,6 +78,11 @@ struct goal2sat::imp {
         m_default_external(default_external) {
         updt_params(p);
         m_true = sat::null_bool_var;
+        sat::extension* e = m_solver.get_extension();
+        if (e) {
+            sat::card_extension* ce = dynamic_cast<sat::card_extension*>(e);
+            m_ext = ce;
+        }
     }
         
     void updt_params(params_ref const & p) {
@@ -116,7 +124,7 @@ struct goal2sat::imp {
         return m_true;
     }
 
-    bool convert_atom(expr * t, bool root, bool sign) {
+   void convert_atom(expr * t, bool root, bool sign) {
         SASSERT(m.is_bool(t));
         sat::literal  l;
         sat::bool_var v = m_map.to_bool_var(t);
@@ -147,15 +155,17 @@ struct goal2sat::imp {
             mk_clause(l);
         else
             m_result_stack.push_back(l);
-        return true;
     }
 
     bool convert_app(app* t, bool root, bool sign) {
-        return convert_atom(t, root, sign);
-    }
-
-    bool convert_pb(app* t, bool root, bool sign) {
-        
+        if (m_ext && t->get_family_id() == pb.get_family_id()) {
+            m_frame_stack.push_back(frame(to_app(t), root, sign, 0));
+            return false;
+        }
+        else {
+            convert_atom(t, root, sign);
+            return true;
+        }
     }
 
     bool process_cached(app * t, bool root, bool sign) {
@@ -175,7 +185,8 @@ struct goal2sat::imp {
 
     bool visit(expr * t, bool root, bool sign) {
         if (!is_app(t)) {
-            return convert_atom(t, root, sign);
+            convert_atom(t, root, sign);
+            return true;
         }
         if (process_cached(to_app(t), root, sign))
             return true;
@@ -195,7 +206,10 @@ struct goal2sat::imp {
                 m_frame_stack.push_back(frame(to_app(t), root, sign, 0));
                 return false;
             }
-            return convert_atom(t, root, sign);
+            else {
+                convert_atom(t, root, sign);
+                return true;
+            }
         case OP_XOR:
         case OP_IMPLIES:
         case OP_DISTINCT: {
@@ -205,7 +219,8 @@ struct goal2sat::imp {
             throw_op_not_handled(strm.str());
         }
         default:
-            return convert_atom(t, root, sign);
+            convert_atom(t, root, sign);
+            return true;
         }
     }
 
@@ -361,6 +376,95 @@ struct goal2sat::imp {
         }
     }
 
+    void convert_pb_args(app* t, sat::literal_vector& lits) {
+        unsigned num_args = t->get_num_args();
+        unsigned sz = m_result_stack.size();
+        for (unsigned i = 0; i < num_args; ++i) {
+            sat::literal lit(m_result_stack[sz - num_args + i]);
+            if (!m_solver.is_external(lit.var())) {
+                sat::bool_var w = m_solver.mk_var(true);
+                sat::literal lit2(w, false);
+                mk_clause(lit, ~lit2);
+                mk_clause(~lit, lit2);
+                lit = lit2;
+            }
+            lits.push_back(lit);
+        }
+    }
+
+    void convert_at_least_k(app* t, rational k, bool root, bool sign) {
+        SASSERT(k.is_unsigned());
+        sat::literal_vector lits;
+        unsigned sz = m_result_stack.size();
+        convert_pb_args(t, lits);
+        sat::bool_var v = m_solver.mk_var(true);
+        sat::literal lit(v, sign);
+        m_ext->add_at_least(v, lits, k.get_unsigned());
+        TRACE("sat", tout << "root: " << root << " lit: " << lit << "\n";);
+        if (root) {
+            m_result_stack.reset();
+            mk_clause(lit);
+        }
+        else {
+            m_result_stack.shrink(sz - t->get_num_args());
+            m_result_stack.push_back(lit);
+        }
+    }
+
+    void convert_at_most_k(app* t, rational k, bool root, bool sign) {
+        SASSERT(k.is_unsigned());
+        sat::literal_vector lits;
+        unsigned sz = m_result_stack.size();
+        convert_pb_args(t, lits);
+        for (unsigned i = 0; i < lits.size(); ++i) {
+            lits[i].neg();
+        }
+        sat::bool_var v = m_solver.mk_var(true);
+        m_ext->add_at_least(v, lits, lits.size() - k.get_unsigned() + 1);
+        if (root) {
+            m_result_stack.reset();
+            mk_clause(sat::literal(v, sign));
+        }
+        else {
+            m_result_stack.shrink(sz - t->get_num_args());
+            m_result_stack.push_back(sat::literal(v, sign));
+        }        
+    }
+
+    void convert_eq_k(app* t, rational k, bool root, bool sign) {
+        SASSERT(k.is_unsigned());
+        sat::literal_vector lits;
+        convert_pb_args(t, lits);
+        sat::bool_var v1 = m_solver.mk_var(true);
+        sat::bool_var v2 = m_solver.mk_var(true);
+        sat::literal l1(v1, false), l2(v2, false);
+        m_ext->add_at_least(v1, lits, k.get_unsigned());        
+        for (unsigned i = 0; i < lits.size(); ++i) {
+            lits[i].neg();
+        }
+        m_ext->add_at_least(v2, lits, lits.size() - k.get_unsigned() + 1);
+        if (root) {
+            m_result_stack.reset();
+            if (sign) {
+                mk_clause(~l1, ~l2);
+            }
+            else {
+                mk_clause(l1);
+                mk_clause(l2);
+            }
+            m_result_stack.reset();
+        }
+        else {
+            sat::bool_var v = m_solver.mk_var();
+            sat::literal l(v, false);
+            mk_clause(~l, l1);
+            mk_clause(~l, l2);
+            mk_clause(~l1, ~l2, l);
+            m_result_stack.shrink(m_result_stack.size() - t->get_num_args());
+            m_result_stack.push_back(l);
+        }
+    }
+
     void convert(app * t, bool root, bool sign) {
         if (t->get_family_id() == m.get_basic_family_id()) {
             switch (to_app(t)->get_decl_kind()) {
@@ -376,13 +480,34 @@ struct goal2sat::imp {
             case OP_IFF:
             case OP_EQ:
                 convert_iff(t, root, sign);
-            break;
+                break;
             default:
                 UNREACHABLE();
             }
         }
-        else if (t->get_family_id() == pb.get_fid()) {
-            NOT_IMPLEMENTED_YET();
+        else if (m_ext && t->get_family_id() == pb.get_family_id()) {
+            switch (t->get_decl_kind()) {
+            case OP_AT_MOST_K:
+                convert_at_most_k(t, pb.get_k(t), root, sign);
+                break;
+            case OP_AT_LEAST_K:
+                convert_at_least_k(t, pb.get_k(t), root, sign);
+                break;
+            case OP_PB_LE:
+                SASSERT(pb.has_unit_coefficients(t));
+                convert_at_most_k(t, pb.get_k(t), root, sign);
+                break;
+            case OP_PB_GE:
+                SASSERT(pb.has_unit_coefficients(t));
+                convert_at_least_k(t, pb.get_k(t), root, sign);
+                break;
+            case OP_PB_EQ:
+                SASSERT(pb.has_unit_coefficients(t));
+                convert_eq_k(t, pb.get_k(t), root, sign);
+                break;
+            default:
+                UNREACHABLE();
+            }
         }
         else {
             UNREACHABLE();